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Author Topic: antenna conversion  (Read 501 times)
KC9BUH
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Posts: 16




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« on: July 23, 2008, 11:52:27 AM »

Has anyone any exerience converting a 1/2 wave-2 5/8 wave (larson 2/70,diamond 73,etc) open coil antenna to operate on GMRS(462.550-467.550)?
I have plenty of ham antennas to play with.
Thanks
Mike
KC9BUH
WQFR960
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K0BG
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Posts: 9896


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« Reply #1 on: July 23, 2008, 11:56:29 AM »

You might be able to, but why not just use on made for the purpose? A 1/4 wave works fairly well, even in a suburban area.

Alan, KØBG
www.k0bg.com
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KC9BUH
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Posts: 16




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« Reply #2 on: July 23, 2008, 01:48:42 PM »

Well I was wondering if anyone had tried it and which side of the open coil whip to trim,if not both sides.I have plenty of extra antennas to play with.
Does the 440 portion radiate from the top?
I posted in a couple of forums in case SOMEONE ONLY READ ONE OF THE TWO FORUMS.
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KB1LKR
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Posts: 1898




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« Reply #3 on: July 23, 2008, 04:00:44 PM »

If it's 2X 5/8 wave at 440-450 MHz (~67.5 cm actual in free space, perhaps a little shorter in an antenna whip)  I'd assume it's 5/8 wave (~16.5") above the open coil and 5/8 wave (~16.5") below the coil.

Your looking for 462-468 MHz (~65.5 cm in free space), so 5/8 wave's about 16" -- you might try shortening each end by ~1/2" (1" total reduction) and see what you get on a UHF antenna analyzer. The air coil inductance might want to be tweaked a little too though. Do you have a UHF/VHF antenna analyser?

If you have a bunch, the economical solution might be to sell them on E-bay and buy 1/4 wave whips cut to the 460's or if you need 70cm too I think Antennex makes some wide bandwidth whips (see Tessco or other distributor).   OTOH if you like experimenting, then go nuts.
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KC9BUH
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Posts: 16




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« Reply #4 on: July 23, 2008, 05:30:16 PM »

Thank you sir for responding to my question. That makes sense to me,so when the time comes I'll try it.
Mike
KC9BUH
WQFR960
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